Weird background on tab row when using standard tab layout

Version 0.99.128.2.1-rc (WebKit 619.1.11.111.2)

Sonoma (14)

You can see some grey background appearing when a new tab is opening/closing

Are you referring to this?

That is just how the tab bar works on macos. you can see the same thing in safari.

eirk Perhaps, it is, when you create or close a tab between already opened there is a grey background:

Comparison with Safari:

Use the Standard tab layout
Set new tabs to open with Start Page
Create a few tabs using Cmd+T or using the toolbar button. You'll notice that the divider between the tabs has a visual bug/flicker. See video below:

The visual flicker should not be there.

Version 0.99.129-beta (WebKit 619.1.11.111.2)

Sequoia (15)